Project Summary Carbon nanotubes (CNT) are shown to damage pleural and peritoneal mesothelial cells which in turn can trigger a compensatory proliferative response, inflammation, mesothelial-to-fibroblastic transition (MFT), fibrosis, and malignant mesothelioma (MM). As their use is constantly increasing, it is important to understand the mechanism of pathogenesis using a relevant model so as to prevent a new asbestos-like problem. In this proposal we will focus on revealing new mechanisms for SWCNT or MWCNT-induced mesothelial cell fibrosis and MM using an oropharyngeal aspiration model of fiber exposure. We propose that CNT exposure causes stress to the endoplasmic reticulum resulting in increased unfolded protein response (UPR) and inflammasome activation. Cytokines released during this process can cause MFT, fibrosis, and MM (Aim 1 a & b). For Aim 1a, we will use pleural and peritoneal human primary mesothelial cells as well as mouse mesothelial cells. Cells will be exposed to equal particle surface area concentrations of asbestos (positive control), SWCNT, MWCNT, or carbon black (negative control) for different time periods, and then UPR and inflammasome activation will be determined. To understand the role of UPR under in vivo conditions, in Aim1b we will use inositol requiring enzyme 1a (IRE1?) conditional knockout (KO) mice crossed to Cre-wt1 mice for specific knockdown of the IRE1? gene in mesothelial cells, since our preliminary data indicate that IRE1? is the UPR upregulated by MWCNT in mesothelial cells in vitro and in vivo. An oropharyngeal aspiration model of exposure and IRE1? KO mice will be used to assess inflammation and fibrosis and an intraperitoneal injection model will be used to study MM. Outcomes are expected to not only reveal new mechanisms of CNT-induced mesothelial diseases, but also to be informative regarding the hazards associated with MWCNT/SWCNT exposure and in developing new therapies for fibrosis and MM.